Heterogeneous fiberous structured Mg-Zn-Zr alloy with superior strength-ductility synergy

Abstract

• The heterogeneous fiberous structured ZK60 Mg alloy was obtained by conventional extrusion method with high yield strength of ∼ 345 MPa, ultimate tensile strength of ∼ 370 MPa and high tensile strain of ∼ 20.5%, superior than most ZK60 Mg alloys reported so far. • The excellent mechanical properties were mainly attributed to the heterogeneous fiberous structure that was characterized by alternating coarse- and fine-grain layers, nanoscale precipitates and profuse < c + a > dislocations. The novel heterogeneous fiberous structured ZK60 Mg alloy have achieved superior strength-ductility synergy. • A novel design of alternating coarse- and fine-grain layered structure was considered to be a general strategy for promoting the strength-ductility synergy of hexagonal close-packed (hcp) metals. Here we reported a heterogeneous fiberous structured Mg-5.6Zn-0.6Zr (wt%) alloy obtained by conventional extrusion method, which exhibited high yield strength of ∼ 345 MPa, ultimate tensile strength of ∼ 370 MPa, and high tensile strain of ∼ 20.5%, superior to most of the Mg-Zn based alloys reported so far. The extraordinarily high mechanical properties were mainly attributed to the heterogeneous fiberous structure consisting of alternating coarse- and fine-grain layers. Grains in the different layers grew into the neighboring layers, ensuring a good layer bonding. A high Schmid factor and geometric compatibility factor for pyramidal slip led to full slip transfer between the neighboring coarse grains and fine grains, which could help to release the stress concentration and avoid early fracture. The profuse activated <c + a> glide dislocations could render the unprecedented high tensile strain. The constraint by the hard fine-grain domains made the soft coarse-grain domains strong like the hard fine-grain domains, as well as the nanoscale precipitates pinning dislocations, contributed to the high strength. The heterogeneous microstructure design was shown to have synergistic improvement in strength-ductility balance, which could be an inspiring strategy to improve mechanical properties of hexagonal close-packed (hcp) metals.